1. Field of the Invention
The present invention pertains to wheel aligning (i.e., wheel alignment measuring) systems, and more particularly, to a system for measuring front wheel toe of the type which includes a wheel mounted projector that provides a mechanically-swept light beam which is intercepted by photo-sensitive means for providing signals that can be employed to indicate wheel toe.
2. Description of the Prior Art
Many prior wheel aligners require accurate positioning of the vehicle relative to a target or the accurate relative positioning of mirrors relative to the vehicle, etc. to provide the relevant wheel alignment data. As will be seen, the wheel aligner of the present invention is of the type wherein all of the data is provided by instruments mounted on the vehicle wheels so that the position of the vehicle relative to its surroundings is immaterial.
The "Angular Position Transducer Apparatus" shown in U.S. Pat. No. 3,782,831 to Senften, issued Jan. 1, 1974, measures separately the individual toe of each front wheel by using a separate projector mounted on each front wheel. In the system described in this patent, taking one front wheel as an example, a light beam projector is mounted on that wheel, and a photocell is incorporated in the projector that is mounted on the other front wheel. The entire light beam projector on said one wheel is mechanically oscillated by a motor driven cam, and the motor simultaneously mechanically rotates a potentiometer which provides a continuously increasing voltage signal that is analogous to the angle through which the beam is swept. The usable, or search angle portion of beam sweep is the sweep, in one direction only, from a reference line through 240.degree. of cam rotation. When the beam, being swept through its search angle, is intercepted by the photocell on the opposite wheel, it has swept in one direction through the angle to be measured, and the corresponding potentiometer voltage is converted by electric circuitry into a toe reading for the wheel upon which the projector is mounted, which reading corresponds to the aforesaid angle measured by the projector.
In order to measure toe of the opposite wheel, a similar projector is mounted on that wheel and a photocell is incorporated in the projector on the first wheel. The second projector measures the individual toe of the wheel upon which it is mounted in the same manner as that previously described. Thus, all of the measuring instruments are wheel mounted in the aforesaid Senften patent; but, in order to measure the toe of both wheels, two oscillating projectors are required (one for each front wheel), and both projectors employ rotating potentiometers as the basic means for developing a voltage which is the analog of wheel toe angle as mechanically measured by the potentiometers.